Exodus 17:9-13

Moses said to Joshua, “Choose men, go out, and fight the Amalekites. Tomorrow I will stand on the top of the hill with the staff of God in my hand.” So Joshua did as Moses said, and fought the Amalekites, while Moses, Aaron and Hur went up to the top of the hill. When Moses held up his hand, Israel prevailed. But when he let down his hand, the Amalekites prevailed. Moses’ hands grew heavy, so they took a stone, put it under him, and he sat down. Aaron and Hur held up his hands, one on each side. So his hands were steady until the sun went down. So Joshua overpowered the Amalekites and his army with the edge of the sword.